This invention relates to a system for monitoring the pressure in a tire and indicating to a vehicle operator an abnormal tire pressure condition.
A number of devices are known for use with pneumatic vehicle tires for monitoring the pressure inside the tire and transmitting information to a remote receiver. For example, U.S. Pat. No. 3,713,092 discloses a cylindrical device that is screwed onto a tire valve stem that transmits a radio signal in response to a low tire pressure condition. Similar devices are disclosed in U.S. Pat. Nos. 4,037,192 and 4,048,614.
These prior art devices have not been widely commercialized for a number of reasons. Many of the devices require mounting inside of a tire or inner tube or on the wheel, and are thus difficult to service and monitor. Other devices, which are mounted on the valve stem, are easily stolen, lost, or vandalized. Battery life in this type of device has been quite limited; hence, the absence of a signal has not necessarily meant the condition of the tire was satisfactory. The battery life problem is exacerbated by the fact that when a low tire pressure condition occurs, the load placed on the battery by the transmitter rapidly drains the battery and renders the device inoperable.
Still another problem is the difficulty in prior art systems of determining which tire is low. This difficulty is particularly acute with large commercial vehicles, which often have eighteen or more wheels.
Accordingly, it is an object of the present invention to provide a tire pressure warning system that notifies the user both when a tire is low and when the battery is low. It is another object of the present invention to provide a tire pressure warning system that facilitates determination of which tire has a low pressure condition. Still another object of the present invention is to provide a tire pressure transmitter that causes very low battery drain.
Another object of the present invention is to provide a very small transmitter package that can be mounted on the valve stem of the tire.
Yet another object of the present invention is to provide a theft-deterrent system for the transmitter.
Another object of the present invention is to provide a transmitter that can easily be tested.
Still another object of the present invention is to provide a completely sealed tire pressure transmitter that can easily be turned on and off without disturbing that seal.